1. Field of the Invention
This invention relates to erosion prevention of hydraulic nozzles for rock bits.
More particularly, this invention relates to a means to prevent erosion as well as a means to securely retain a nozzle body within a nozzle body recess cavity by providing a nozzle retainer that resists loosening due to vibration and inhibits erosion of the nozzle retainer and its surrounding nozzle recess cavity during operation of a rock bit in a borehole.
2. Description of the Prior Art
There are a number of prior art inventions that deal with the retention of a nozzle flow bean within the body of a rotary cone rock bit or a drag type earth boring rock bit.
U.S. Pat. No. 3,084,751 teaches an erosion resistant nozzle body or "bean" that is retained within the dome portion of a rotary cone rock bit by utilizing a nail retention method. A circumferential groove is formed in the outside wall of the nozzle body that mates with a registering groove formed in the rock bit body. The flow bean is inserted in a nozzle cavity and a nail enters tangential to the registering channels formed between the exterior of the nozzle flow bean and the rock bit body such that the nail, when driven in place, fills the slot between the flow bean and the body, thereby retaining the flow bean in the body. A rubber O-ring is positioned upstream of the nail retention device to prevent erosion of the retention nail from the interior of the rock bit body.
This type of nozzle body retention is disadvantaged in that the nozzles are difficult to remove from their nozzle retention cavities. Additionally, erosion occurs at the exit end of the nozzle and attacks the nail retention device and may eject the nozzle body from the rock bit if sufficient erosion occurs to destroy the nail retaining the nozzle within the body.
U.S. Pat. No. 3,129,777 describes an erosion resistant nozzle body that is retained within the body of a rock bit by expanding rings that register with aligned arcuate slots into the nozzle body walls. Half snap-type rings are positioned on 180.degree. locations on the exterior of a nozzle retaining sleeve. When the nozzle retention sleeve is inserted in the nozzle cavity to a depth where the support rings are aligned with the opposing notched arcuate slots, the nozzle retention body is locked in place. To remove the sleeve and flow bean, the sleeve is rotated 180.degree. to enable the split rings to disengage with the opposite aligned slots in the rock bit body.
This device is extremely complex in that partial arcuate grooves must be formed within the rock bit body at positions 180.degree. one from the other so that the half snap rings extending from the nozzle retainer sleeve may be aligned with the registering slots in the body. This is a difficult and expensive operation and requires very precise machining.
U.S. Pat. No. 3,220,754 describes yet another means to retain an erosion resistant nozzle body within a rock bit body. This invention describes a method wherein a roll-type pin is used to retain the nozzle bean within the rock bit body. A slot is formed in the erosion resistant nozzle body that aligns with a drilled hole in the rock bit body and, when the slot registers with the hole in the body, a pin is driven into the aligned opening. The end of the pin is diverted through a hole drilled at an angle to the registering hole so that the end of the pin is bent, thereby retaining the pin within the slot of the nozzle bean to retain the bean within the rock bit body.
This type of nozzle retention is disadvantaged in that the pin is difficult to remove from the rock bit body for replacement or removal of the nozzle body.
Finally, U.S. Pat. No. 4,381,825 teaches yet another means to retain an erosion resistant nozzle flow bean within the body of a rock bit. This patent teaches a flow bean nozzle body having a threaded bean retention sleeve metallurgically bonded to the exterior surface of the nozzle. The erosion resistant nozzle is threaded within complementary threads in a nozzle retention cavity formed in the body of the rock bit.
This type of nozzle retention is disadvantaged in that vibration and hydraulic flow through the nozzle may loosen the threads of the nozzle body. The nozzle may then be ejected from the face of the rock bit. A metal sleeve may be interference fitted within the nozzle cavity by driving the sleeve down against the outer peripheral edge of the exit end of the nozzle body to prevent the threaded nozzle from backing out of its threaded nozzle retention bore. The metal retention sleeve however is extremely difficult to remove to replace the nozzle threaded into the nozzle retention cavity.